Thanks to ptl on the IRC, it seems that the PR1.2 SDK has been put up.PR1.2 HAS NOT BEEN RELEASED, STOP ASKING ABOUT IT, ONLY THE CHANGES ARE LISTEDOh hey, it was released in May after all, well, I doubt anyone will see this edit since it's been released :P ~ Aug, 29

Upgraded and installed, changes for now:

Virtual keyboard has been redone.

Menu is now rearrangable, and there is no more "More..."

Clear device is back in Settings.

The gap in the menus and status bar have been removed (top gap) - Edit: Might be SDK specific since the status bar isn't exactly the same as on the device.

Browser now has a back button, history view is accessible using the gesture.

Enable rotation is now an option in Settings (Browser).

Volume buttons can be set to change volume only in browser.

User Guide accessible in the browser from a main menu shortcut.

Media player has a play button icon instead of the moving bars (bottom right area)

Ovi Store link in "Change background" and "Themes" area.

Browser seems much much snappier, scrolling is quick and rendering is uber quick! Not sure if this is related to the much faster processor but the gecko engine was updated.

File manager has a share option for all files.

Video call option can now be enabled in contacts, SMSs to landlines can be disabled, voicemail number can be set.

Typing in Application Manager searches for applications (same speed as in contacts in the SDK)
Another change in the App Manager is that there's an update all button in the Update section.http://www.youtube.com/watch?v=XjAwC4nM5cE

Browser will have three buttons in portrait mode, back, add bookmarks, and bookmarks (bookmarks not showing in screenshot but it should be there in PR1.2)

Software Development Kit, basically it's a cross compiler so you can compile software for Maemo, it's used for development.
The SDK has an emulator so I can see the UI of Maemo 5 (and hence the changes)